Photographic processes and products



May 2;1961 E. H. LAND PHOTOGRAPHIC PROCESSES AND PRODUCTS Filed July 22, 1955 FIG. 2

AITORNEYS United States Patent PHOTOGRAPHIC PROCESSES AND PRODUCTS Edwin H. Land, Cambridge, Mass., assignor to Polaroid Corporation, Cambridge, Mass.,a corporation of Delaware Filed July 22, 1955, Ser. No. 523,885

5 Claims. (Cl. 96-76) sheets.

A variety of photographic processes may be effected by spreading a composition in a uniformly thin layer between a pair of superposed sheets. For example, a photosensitive stratum supported on one of the sheets may be developed by a processing composition spread between it and another sheet. Here, spreading may be effected after photoexposure to develop an existing latent image or before photoexposure so that a latent image foimed immediately thereafter develops spontaneously. Alternatively, a photosensitive composition may be spread between the sheets in the presence of a developer to provide a stratum which, when photoexposed shortly after being formed, receives a latent image that develops spontaneously.

It has been the practice to spread the composition between the sheets by means of specially designed pressureapplying members such as precisely aligned and carefully fabricated rollers. Often, either it is found that these are too costly for the purpose contemplated, or it is intended that they be omitted from the apparatus provided. The present invention makes it possible to'spread the composition between the sheets either by pressure-applying members of indifferent design or by hand.

The present invention contemplates the use of rigid sheets which are not deformed when the composition is spread between them. For example, these sheets, as components of a film unit comprising a container of composition for discharge between them, may be pressed together in any suitable way without deformation until a given distance apart. Alternatively, their spacing may be predetermined when the film unit is manufactured so that the composition may be drawn between them by capillary action. The distance between the sheets preferably is controlled by spacers interposed between them before or during spreading. These'spacers may be so composed as to dissolve in the composition after spreading to permit collapse of the sheets toward each other as the composition dries.

The present invention is applicable to a variety of proccesses involving the formation of latent images in dispersions of heavy metal salts such as the noble metal salts, particularly the silver halides. It is particularly applicable to processes of the silver transfer-reversal type. In such a process, a photoexposed silver halide stratum is treated between two sheets by a silver halide developer and a silver halide solvent. The reagents reduce ex posed silver halide to silver and react with unreduced silver halide to form a solublesilver complex which, in turn, is reduced to silver in a silver-receptive environment. This silver-receptive environment may be either distinct from or interspersed with the silver halide. The positive print so formed is retained permanently between the sheets.

, It has been the practice to separate the silver halide from the silver-receptive environment after the positive.

print has been formed. The fact that they may be retained together permanently has been recognized by.

Edwin H. Land in One Step Photography, Photographic Journal, Section A, pages 7-15, January 1950, where it is '7 indicated that the silver-receptive environment may be of reduced silver. As disclosed in US. Patent No. 2,861,-

' 885, issued to Edwin H. Land on November 25, 1958, if

the silver halide is in such concentration as to give rise only when fully developed to a predeterminedly low maximum density and if the silver complex is reduced to silver in a vigorous silver-receptive environment of the foregoing type, the resulting negative and positive prints, in registration, provide a composite print that presents a good image by reflection or projection, depending on whether one or both of the two supports are transparent. Accordingly, objects of the present invention are; to provide a photographic process for treating an exposed photosensitive stratum by spreading a fluid composition between a pair of rigid sheets; toprovide a photographic process of the foregoing type wherein spreading is accomplished by pressing a pair of rigid sheets together; to provide a photographic process of the foregoing type wherein spreading is accomplished by capillary action between a pair of rigid sheets predeterminedly spaced apart; to provide a photographic process of the foregoing type wherein spacers are provided for controlling the'distance between the sheets; to provide a photographic process ofrthe foregoing type wherein the spacers, soluble in the composition, permit the sheets after spreading to collapse toward each other as the composition dries; to provide a photographic process of the foregoing type wherein the sheets are maintained in permanent superpositionafter spreading; and to provide photographic products useful in effecting processes of the foregoing type.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of theothers, and the product pos sessing the features, properties and the relation of .el

ments which are exemplified-in the followingdetailed disclosure, and the scope of the application of whichiwill be indicated in the claims.

panying drawing wherein:

Figure 1 is an exaggerated perspective view of a photographic product for effecting a process of the present 'invention;

Fig. 2 is an exaggerated sectional view of the product of Fig. l in use; a Fig. 3 is an exaggerated perspective view, partly broken away, of another photographic product for effecting a process of the present invention; and

Fig. 4 is an exaggerated sectional view of the productof ii Fig. 3 in use.

GENERAL DESCRIPTION or FILM UNITS HERE- INAFTER SPECIFICALLY DESCRIBED V Generally, each of the film units hereinafter specifically described comprises two rigid sheets at least one of which is transparent. These sheets are eithersuperk posed or adapted to be superposed a predetermined, distance apart. When such a film unit is in operatio' j a silver halide composition is subjected, between the sheets, to 'a silver halide developer and a silver halide solvent in order to elfect silver transfer eVersaIQJJn 2,982,650 Patented May 2, 1961 t acsaeeo practice, one or more of these materials are made available at any of a variety of locations in the film unit, for example dispersed in dry condition on one or both of the sheets. The arrangement is such that the developer and solvent do not act upon the silver halide composition until an aqueous fluid, which may or may not contain one or more of these materials, is spread between the sheets. The aqueous fluid may be supplied either from a rupturable container carried by the film unit or from an external source. The sheets are retained in superposition permanently so that they form a protective barrier against harm to or defacement of the print as a result of reaction of exhausted or unexhausted reagents with atmospheric oxygen and/or reaction of reduced silver with atmospheric sulfides such as sodium sulfide and environmental contaminants such as atomic sulfur.

One film unit of this type is so arranged that its two sheets are pivotally connected, a photosensitive silver halide stratum being carried on one of the sheets, a

silver-receptive stratum on the other and an aqueous alkaline solution of a silver halide developer and a silver halide solvent being carried in a container that discharges its contents for spreading between the sheets when they are pressed together manually.

Another similar film unit carries in its container at photosensitive composition to be spread between the two pivotable sheets in the presence of a developer to provide a stratum which, when photoexposed shortly following its formation, receives a latent image that develops spontaneously. In this product, the developer may be carried in a variety of ways, for example dispersed in dry condition on one of the sheets. This film unit requires no shielding from environmental light until the photosensitive composition is ejected from the container. Ejection may take place within the exposure chamber of a camera where the photosensitive composition forms a photosensitive stratum which, when photo exposed through one of the sheets, receives a latent image from which a useful print is formed without further manipulation or treatment.

Another film unit of this type is so arranged that the two sheets are prespaced during fabrication. One of the sheets carries a silver halide stratum and the other a silver-receptive stratum. Because their adjacent surfaces are very close together, an aqueous solution into which an end of this film unit is dipped is rapidly drawn into their interstice by capillary action. Any of the silver halide developer, silver halide solvent and even the alkali which are to effect silver transfer reversal may be carried in dry condition on either orboth of the sheets or in the solution to be spread between them.

One or both of the rigid sheets are transparent depending on whether the print to be produced between them is to be viewed by reflected or transmitted light. Suitable materials for this purpose are glass and glasslike organic polymers which are optically clear and water insoluble. Examples of suitable glasslike organic polymers are: acrylates such as methyl methacrylate, cyclohexyl methacrylate, alpha methyl acrylate, and alpha chloroacrylate; styrenes such as alpha methyl styrene and vinyl toluene; cellulosics such as cellulose acetate, cellulose acetate butyrate and ethyl cellulose; vinyl chloride copolymers such as vinyl chloride vinyl acetate; and condensation polymers such as ethylene glycol terephthalic acid polyester sold by Du Pont under the trade name Mylar. Where the composition is to be spread by pressing the sheets together, if desired, it may advantageously have high viscosity, preferably a viscosity ranging from 100 to 200,000 centipoises at a temperature of C. These sheets should have a sufiiciently high modulus of fiexure to resist deformation when pressed together until a few thousandths of an inch apart with the composition of whatever viscosity therebetween. Sheets composed of such glass and glasslike materials have been found to be sufficiently rigid when as little as one-hundredth of an inch thick. For good optical clarity, it is preferred that these sheets be no more than two-tenths of an inch thick.

Figs. 1 and 2 illustrate the mechanical structure of one form of a film unit embodying the present invention. This film unit, generally designated by 20, comprises a pair of rigid transparent sheets 22 and 24 mounted respectively on a pair of frames 26 and 28 which are pivotally connected by a hinge 30. Sheet 22 is shown in Fig. 2 as supporting a stratum 32 which, in one form, contains a photosensitive silver halide. Sheet 24 is shown in Fig. 2 as supporting a stratum 34 which, in one form, contains silver precipitating nuclei. Supported on frame 28 adjacent to hinge is a container 36 carrying an aqueous fluid, shown in Fig. 2 at 38, which, in one form, contains, in aqueous alkaline solution, a silver halide developer and a silver halide solvent. Container 36 is provided with a rupturable mouth 40 through which its contents are ejected when it is subjected to opposed compressional forces. Such forces are exerted when sections 42 and 44 of frames 26 and 28, respectively, are pivoted into juxtaposition. Sheets 22 and 24 are seated for slight movement in the indented medial sections 46 and 48 of frames 26 and 28, respectively, for example, by means of a resilient adhesive 50 such as a rubbery cement. Movement of these sheets toward each other is limited by a pair of spacer strips 52 shown in Fig. 1 as being supported at the longitudinal edges of sheet 24. These strips, preferably ranging from two to six thousandths of an inch in thicknes, are less compressible than adhesive 50 so that they control the spacing between the sheets when frames 26 and 28 are juxtaposed. A pair of ribs 54 in frame 26 are designed to be received by a pair of grooves 56 in frame 28 to prevent composition 38 from flowing laterally beyond the longitudinal edges of the juxtaposed frames. The free ends of frames 26 and 23 are respectively provided with depressions 62 and 64 which, when the frames are juxtaposed, form a reservoir for the reception of excess composition. The free end of frame 28 is provided with a catch 66 that snaps into a notch 68 at the free end of frame 26 to retain the frames in permanent juxtaposition.

Container 36, in one form, is constructed from a blank of three-ply sheet material having a single fold. The outer ply serves as a backing or support and is composed of a thin, relatively inexpensive, tough material, preferably a paper, such as kraft paper. The intermediate ply is composed of a substantially vaporand liquid-impervious material, for example, a metal foil such as aluminum or lead foil. The inner ply is composed of a thermoplastic or thermosetting plastic material, for example, a polyvinyl acetal such as polyvinyl butyral or polyvinyl formal, which protects the container contents from contamination. A composition comprising by weight approximately to 70% polyvinyl butyral, approximately 10 to 23% of nitrocellulose and approximately 5% dibutyl sebacate is particularly satisfactory. At opposite end portions of the container, the two folds of the inner ply are sealed to each other by the application of heat and pressure. Those two sections of the twofold defining mouth 40 are bonded together by a strip of adhesive so constituted that the bonding forces be tween it and the inner ply are less than the cohesive forces between end portions of the inner ply that are sealed together. A satisfactory strip may be composed, for example, of ethyl cellulose or a mixture of ethyl cellulose and paraffin, the mixture including at least 50% by weight of ethyl cellulose. Since the bonding forces between those sections defining the mouth are less than a ess "5 the bonding forces between other sectionsof the con: tamer, the application of opposed compressional forces to the container causes discharge of the containers contents through its mouth.

Fig. 2 illustrates the film unit of Fig. 1 in use with frames 26 and 28 locked in juxtaposition by catch 66 and notch 68. Solution 38 is shown as having been ejected from container 36 and spread between strata 32 and 34 in a thin layer. Stratum 32 which, as stated above, in one form. contains silver halide, is photoexposed either before or immediately after this spreading is effected. Solution 38, as stated above, in. one form contains a developer which reduces exposed silver halide in stratum 32 to silver, and a silver halide solvent which reacts with unreduced silver halide to form a com plex silver salt that diffuses to stratum 34 where, in the presence of unexhausted silver halide developer and a silver precipitating agent, it is reduced to silver. The period initiated by spreading solution 38 and terminated by completing negative formation 'in stratum 32 and positive formation in stratum 34 ordinarily ranges from 40 to 120 seconds in duration.- I In accordance with the present invention, the solution thereafter is dried in order to form a more or less solid residue that serves as an adhesive to bond the sheets together.

In order to dry the solution rapidly, where sheets 22 and 24 are water impermeable, in a modification of the film unit of Fig. 1, there is interposed between sheet 22 and stratum 32 and/or between sheet 24 and stratum 34 a thin. moisture-absorbent stratum composed, for example, of gelatin. As indicated above, the silver halide in stratum 32 is in such concentration as to give rise only when fully developed toa'predeterminedly low maximum density, and the silver precipitating environment of stratum 34 is so vigorous that the resulting nega tive in stratum 32 and positive in stratum 34in superposition provide a composite print that presents a good positive image by reflection or projection. V

Strips 52, in one form, are soluble in composition 38 so that, as moisture in the layer of composition evap orates, sheets 22 and 24 collapse towardeach other, adhesive 50 being designed to expand, as well as to contract, so as not to hinder this collapse.

The above description for clarity has referred to the mechanical structure of Figs. 1 and 2 in relation to a silver transfer-reversal process wherein an alkaline aqueous solution of a silver halide developer and a silver halide solvent is spread between a silver halide stratum and a silver-receptive stratum. A description of the chemical composition of various materials suitable for such use follows:

In one form of stratum 32, one or more of the silver halides, of which silver chloride, silver bromide and silveriodide are examples, are dispersed in a suitableprotective colloid material, for example, gelatin, agar, albumen, casein, collodion, a cellulosic such' as carboxymethyl celluloseya vinyl polymer such as polyvinyl al cohol or a linear polyamide such as polyhexamethylene adipamide. Examples of specific formulations 'of 'conventional emulsions suitable for such use are described %in T. T. Baker, Photographic Emulsion Technique,

erican Photographic Publishing Company, Boston, 1:948, chapter IV.

-,In one form, composition 38 is an aqueous alkaline solution of a silver halide developer and a silver halide solvent. ,The solution also contains a film-forming material such as a water-soluble polymer, starch or gum for imparting a viscosity of 100 to 200,000 centipoises at a temperature of 20 C. Suitable developers are:,benzene derivatives having at least two hydroxyl and/or amino groups substituted inortho or para position on the ben-v zene nucleus, such as hydroquinone, amidol, metol, glycin, "p -aminophenol and pyrogallol; and hydroxylamines, inlparticular, primary and secondary aliphatic. and aromatic N-substituted or fi-hydroxylamines which 6 t are so le v queonsalkali. ludi yd o y amine. N-methyl hydroxylamine, N-ethyl hydroxylamine,.and

others described in application Serial No. 470,802, filed November 23, 1954, now U.S. PatentNo. 2,857,276 in the name of Edwin H; Land et a1. 7 Suitable silver halide solvents are: conventional fixing agents such as sodium thiosulfate, sodium thiocyanate, ammonium thiosulfate and others described in Patent No. 2,543,181, issued to Edwin H. Land on February 27, 1951; and associations of cyclic imides and nitrogenous bases such as associations of barbiturates or uracils, and ammonia'or amines, and other associations described in application Serial, No. 378,684, filed September 4, 1953, now U.S. Patent No. 2,857,274, in the name of Edwin H. Land et al.

In one form, stratum 34 providesvone of the vigorous silver precipitating environments described in Patents Nos. 2,698,237 and 2,698,245, which issued to Edwin H. Land on December 28, 1954. Such an environment includes silver precipitating nuclei such as the metal sulfides or selenides, the colloidal noble metals or organic thio compounds dispersed in a macroscopically continuous vehicle comprising minute particles of a watersoluble, inorganic, preferably siliceous, material such as silica aerogel. Preferably this stratum ranges from 1 to 8 microns in thickness. The positive print is formed in the stratum from fine silver particles concentrated primarily at its surface. Only a minute amount of silver in this condition is necessary for image formation because'of its extremely high covering power.

The covering power of silver in a photographic print depends in part upon the concentration arrangement, size and shape of the silver grains. In a composite print, produced as above, the silver deposited by development in stratum 32 is characteristically different from the silver deposited'by silver complex transfer and reduction in stratum 34. In practice, the covering power of a given mass of silver in the positive of silver-receptive stratum 34 ranges from 4 to 15 times that of an equal mass of silver in the negative of silver halide stratum 32.

It is apparent that the minimum density of the composite print depends to a substantial extent upon the maximum density of the negative since the shadows of V the negative correspond to the highlights of the positive.

If the above noted ratio of positive silver covering power to negative silver covering power is realized in a composite print to be viewed by reflection, this maximum negative density can be as great as 0.3 without seriously affecting the composite image quality. A substantially higher maximum density is tolerable in the negative when the composite print is used as a transparency because the brightness of the highlights of the composite image is a function of the intensity ofillumination. It has been found that a maximum density of no greater than 1.0

in the negative is permissible if the maximum density of the composite print is at least four times greater. For

best results, then, in a composite image of the foregoing type, the silver halide stratum, when fully developed in any conventional manner, has no greater density than approximately 0.3 if' the composite print is to present a I reflection image, and has no greater density than approximately 1.0 if the composite print is to serve as a transparency.

ALTERNATIVE FORMS O'F FILM UNIT OF FIGS.

1 AND 2 IN WHICH PHOTOSENSITIVE SILVERv HALIDE COMPOSITION IS SPREAD BETWEEN SHEETS IN THE PRESENCE OF A SILVER HAL? -IDE DEVELOPER AND A SILVER HALIDE SOL- VENT As indicated above, the present invention is applicable to a wide variety of processes other than those in which an alkaline aqueous solution of a silver halide developer and a silver halide solvent are spread between the'ad jacent surfaces of a silver halide stratum and a silverreceptive stratum. Inan alternative form, the film unit of Figs. 1 and 2 carries a quantity of at least one of the components of a silver halide composition to be spread between the two pivotable rigid sheets in the presence of reagents including a silver halide developer and a silver halide solvent. Here, the developer and/or solvent either are kept apart from the silver halide composition or are kept together with the silver halide composition in inactive condition. For example, either or both the developer and solvent may be dispersed in dry condition on one or both of the sheets so as not to coact with the silver halide composition until spread. Or, an alkali active developer may be mixed with the silver halide composition and kept in a nonalkaline environment until spread in the presence of an alkali dispresed in dry condition on one or both of the sheets. All of the silver halide composition and the various reagents may be carried in one or more compartments provided by one or more containers. For example, two compartments may be provided to carry separately a silver halide composition and one or more of the components necessary to provide it with a reducing environment. Or, two compartments may be provided to carry separately silver halide components such as a salt having silver cations and a salt having halide anions which do not form a photosensitive compound until mixed. A silver precipitating agent may be dispersed on whichever sheet the transfer image is to form or may be mixed with the silver halide composition when the transfer image is to form in the photosensitive stratum itself. When a short delay between spreading and photoexposing the silver halide composition is desired, development may be postponed, for example by interposing, between the photosensitive stratum and one of the components necessary to the provision of a reducing environment, a temporary barrier such as an alkali-soluble stratum that dissolves in the presence of the reagents after a predetermined delay. It is apparent that the chemical organization within a film unit of this type may be varied as desired in response to a wide variety of requirements.

In accordance with this aspect of the present invention, in one alternative form of the film unit of Fig. 1, composition 33 and stratum 32 are of the following formulations, and stratum 34' is omitted. Composition 38, a gel which is fiuid enough under ambient conditions to be readily spread, is prepared by stirring an aqueous solution of a silver halide developer into a ripened photosensitive silver halide emulsion. The developer is alkali active, i.e., active only in alkaline solution, so that it has no developing effect on the silver halide emulsion in the nonalkaline environment provided by container 36. Examples of developers of this type are pyrogallol, hydroquinone, metol, amidol, p-aminophenol, glycin and pphenylcnediamine. Stratum 32 is prepared from an organic plastic vehicle such as sodium carboxymethyl cellulose into which has been stirred: an aqueous solution of a silver halide solvent, for example, a silver complexing agent such as sodium thiosulfate; an alkali, for example a hydroxide such as sodium hydroxide, a carbonate such as sodium carbonate, a borate such as borax, or a phosphate such as dibasic sodium phosphate; and a silver precipitating agent, for example one or more of the zinc, cadmium and lead sulfides and selenides. Preferably. an anti-oxidant for the developer also is provided. For example, sodium sulfite may be carried by stratum 32 or ascorbic acid by container 36.

When a short delay between spreading and photoexposing the silver halide composition is desired, it is possible to postpone the application of the silver halide developer to the silver halide composition by coating stratum 32 with a material that dissolves or becomes permeable in solution. One such material that dissolves rapidly in alkaline solution is cellulose acetate hydrogen phthalate. When composition 38 is spread, this alkalisoluble stratum is moistened and subjected to dissolution in consequence of the presence of alkali from stratum 8 32. Upon dissolution of this alkali-soluble stratum, silver transfer reversal can occur.

Example In one specific alternative form of the film unit of Fig. 1: composition 38 is prepared by heating 10 cc.

of a moderately high speed gelatino iodobromide emulsion to the liquid state and stirring into it a solution of 0.19 g. of amidol in 1 cc. of water. Approximately 0.7 cc. of the resulting mixture is injected into container 36 from a syringe. Stratum 32 is prepared by treating a silver-receptive stratum containing a silver precipitating agent of the type above described. This stratum, supported on a sheet of baryta paper, is dipped for approximately 20 seconds into an aqueous solution containing by total weight 4.6% of sodium carbonate, 5.7% of sodium sulfite and 3.6% of sodium thiosulfate. The excess solution is doctored from the sheet by a stirring rod and the sheet is thoroughly dried under heat. Sheets 22 and 24 are pressed together in order to spread composition 38 therebetween in the form of a uniform photosensitive layer which is immediately photoexposed. A positive print is visible through the sheets at the end of a 60-second processing period.

In modifications of the alternative form of the film unit of Fig. 1, the various materials are distributed as desired on either or both of strata 32 and 34 or in container 36, provided only that the silver halide in the container is kept from contact with the silver halide solvent and that the alkali-active silver halide developer is kept from contact with the alkali.

In one modification of the alternative form of the film unit of Fig. 1, container 36 carries a silver halide material, stratum 32 contains processing materials and stratum 34 contains silver-receptive materials. These materials are of the type described above, the silver halide material being a gclatino silver halide emulsion, the processing materials including a silver halide developer, a silver halide solvent and an alkali, and the silver-receptive materials including silver precipitating nuclei dispersed in an inorganic, preferably siliceous, vehicle. The silver halide material, when photoexposed immediately after being spread in a layer between strata 32 and 34, receives a latent image from which a positive print develops spontaneously in stratum 34.

In another modification of the alternative form of the film unit of Fig. 1: composition 38 contains a silver halide salt and a silver precipitating agent; stratum 32 contains a silver halide developer, a silver halide solvent and an alkali; and stratum 34 is omitted so that sheet 24 acts merely to spread the composition on stratum 32. Composition 38, for example, may be prepared by stiring a silver precipitating agent, for example silver sulfide, into a silver halide emulsion of the type described above. The alkali, for example, is a carbonate such as sodium carbonate, a borate such as borax, or a phosphate such as a dibasic sodium phosphate. The photosensitive stratum formed when composition 38 is spread, upon being photoexposed, receives a latent image in which,

by silver transfer reversal, a positive print is formed in situ.

It is often desirable, for example when storage of film unit embodying the present invention for a pro.- longed period is expected, to separate the components of the silver halide composition until used. For this pur-' pose, in a further modification of the alternative form photoexposure eceives. a .latent image from,which a positive print forms spontaneously.

Other modifications of the alternative form of the film unit of Fig. 1 in which two-compartment containers are employed will occur to persons skilled in the art. For example, one of the compartments of such'a container may carry a photosensitive composition or one of its componentsand the other a processing composition or one of its components, the remaining components of the photosensitive composition and the processing composition being distributed in strata 32 and 34. Alternatively, the container may provide but one compartment carrying one of the components of the photosensitive composition, for example a salt having halide anions and the other compartments of the photosensitive composition, for example, including a salt having silver cations, may be distributed in either of strata 32 and 34.

In those forms of the film unit of Fig. l in which sepreading is effected before photoexposure, it is possible to provide the outer face of sheet 22, which in this instance is transparent, with an optical screen, for example one of the lenticulated or additive color type. After spreading is effected between the inner face of sheet 22 and sheet 24, the photosensitive stratum is photoexposed through the optical screen. The resulting print, which forms either in silver-receptive stratum 34 or in layer of solution 38 when it incorporates silver precipitating nuclei, is automatically aligned with the optical screen through which the image is viewed.

FILM UNIT OF FIGS. 3 AND 4 WHEREIN FLUID IS SPREAD BETWEEN THE SHEETS BY CAPIL- LARY ACTION As indicated above, in accordance with another aspect of the present invention, the two rigid sheets are prespaced before use. A film unitincorporating such sheets is shown in Figs. 3 and 4 as comprising a pair of sheets 70 and 72, one or both of which are transparent. The adjacent surfaces of sheets 70 and 72 are coated with a pair of strata 74 and 76, stratum 74, in one form, containing a silver-receptive material and stratum 76, in one form, containing a silver halide material. The adjacent surfaces of these strata are spaced from each other by a pair of thin strips 78 and 80. The close spacing of the strata makes it possible for an aqueous fluid 82, in the form of an alkaline aqueous solution of a silver halide developer and a silver halide solvent, to be drawn through their interstice by capillary action, as indicated in Fig. 4, by the rising meniscus 84, from a supply 86, into which an end of the film unit is dipped.

In a modification of this film unit, all of the processing reagents are dispersed in dry condition in either one or both of strata 74 and 76. For example, an alkali-active developer is dispersed in stratum 76 and an alkali and a silver halide solvent in stratum 74 so that water alone, when drawn between the sheets by capillary action, is able to initiate silver transfer reversal.

Strips 78 and 80 are so constructed that aqueous fluid 82 is drawn between them in a layer which ordinarily ranges in thickness from 1 to 6 thousandths of an inch,

\the strips themselves preferably being of this thickness. ,These strips are advantageously of a water-soluble matefrial, in particular of an aqueous alkali-soluble material, such as sucrose or cellulose acetate hydrogen phthalate,

which dissolves in the layer of aqueous fluid during processing to permit sheets 70 and 72 ,to collapse toward each other as the fluid evaporates.

In either of the film units of Figs. 1, 2 and 3, 4 it may be desirable to prevent the various reagents of the composition from being oxidized by contact with the atmosphere and so to discolor or otherwise deface the print. In the case of the film unit of Figs. 1 and 2, frames 26 and 28, in one form, are constructed to so snugly engage each other as to hermetically seal the space between the as titanium dioxide which reduces or eliminates the tendency of the negative to decrease the overall contrast of the composite print.

i It is to be expressly understood that in all of .the abovedescribed products and processes, neither a silver halide solvent nor a silver precipitating agent need be present if it is desired merely to develop a latent image rather than to effect silver transfer reversal. Also, although the present invention is particularly concerned with the processing of a silver halide layer between a'pair of rigid sheets which are relatively positioned during processing by soluble spacers, photosensitive layers such as those containing ferric or diazo compounds may be used in any of the above-described products and processes.

The above description has referred specifically to products for spreading photographic compositions between rigid sheets without the use of specially designed pressure-applying members. Details of the contemplated processes which have not been specifically described will be apparent from consideration of details of the various products specifically described.

Since certain changes may be made in the above process and product without departing from the scope of the invention herein involved, it is intendedrthat all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A photographic product in the form of a film unit comprising a pair of rigid plates, pivot means at one end of said plates constraining said plates for pivotal movement with respect to one another between remote and superposed relative positions, said plates, when in super posed position, defining a thin region therebetween with-' in which an aqueous fluid may be spread in order to process a silver halide salt with a silver halide developer for the production of a visible print, the surface of one of said plates being provided at the lateral margins of said region with a pair of strips for confining said fluid to said region between said plates, at least one of said' plates being transparent to permit observation of said print while said plates are superposed, said film unit I, carrying at least one of said salt and said developer and f a quantity of said aqueous fluid disposed in a rupturable container located adjacent said pivot means between said 1 plates exterior of said region therebetween in which said fluid is spread.

2. The photographic product of claim 1 wherein both I of said rigid plates are composed of transparent glass.

3. A photographic product in the form of a film unit comprising a pair of frames, each of said frames being medially provided with a transparent rigid plate, said plates being provided with medial rigid surfaces recessed with respect to the opposed surfaces of said frames, pivot means constraining said frames for pivotal movement of said surfaces of said plates into superposition with one another, a rupturable container so constructed and cara silver halide solvent in order to produce a visible print,

at least one of said surfaces of said plates and said fluid carrying at least one of said silver halide salts, said silver halide developer and said silver halide solvent.

4. The photographic product of claim 3 wherein at least one of said surfaces of said plates is provided with diflicultly compressible means for limiting movement of the last-mentioned surfaces toward one another.

5. A photographic product in the form of a film unit comprising a pair of frames, each of said frames medially including a transparent rigid plate, said plates providing rigid surfaces at least one of which is recessed with respect to the inner surface of the frame in which it is included, pivot means for pivotally constraining said frames for movement of said surfaces into superposition, one of said surfaces supporting a silver halide stratum, the other of said surfaces supporting a silver-receptive straturn, and a rupturable container mounted between said frames adjacent said pivot means and carrying an aqueous alkaline solution of a silver halide developer and a silver halide solvent for spreading in a thin layer between said surfaces when said frames are pivoted to bring said surfaces into superposition, said container being constructed and arranged for ejecting its fluid contents between said surfaces of said plates when said container is subjected to compressive pressure exerted by pivotal movement of said frames to bring said surfaces into superposition.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES The Photographic Journal, One-Step Photography, Section A, January 1950, pp. 7-15. 

1. A PHOTOGRAPHIC PRODUCT IN THE FORM OF A FILM UNIT COMPRISING A PAIR OF RIGID PLATES, PIVOT MEANS AT ONE END OF SAID PLATES CONSTRAINING SAID PLATES FOR PIVOTAL MOVEMENT WITH RESPECT TO ONE ANOTHER BETWEEN REMOTE AND SUPERPOSED RELATIVE POSITIONS, SAID PLATES, WHEN IN SUPERPOSED POSITION, DEFINING A THIN REGION THEREBETWEEN WITHIN WHICH AN AQUEOUS FLUID MAY BE SPREAD IN ORDER TO PROCESS A SILVER HALIDE SALT WITH A SILVER HALIDE DEVELOPER FOR THE PRODUCTION OF A VISIBLE PRINT, THE SURFACE OF ONE OF SAID PLATES BEING PROVIDED AT THE LATERAL MARGINS OF SAID REGION WITH A PAIR OF STRIPS FOR CONFINING SAID FLUID TO SAID REGION BETWEEN SAID PLATES, AT LEAST ONE OF SAID PLATES BEING TRANSPARENT TO PERMIT OBSERVATION OF SAID PRINT WHILE SAID PLATES ARE SUPERPOSED, SAID FILM UNIT CARRYING AT LEAST ONE OF SAID SALT AND SAID DEVELOPER AND 